1. Field of the Invention
The present invention relates to a compression apparatus for molding which applies compression force to a resin within a die during injection compression molding or press molding. The present invention also relates to an injection compression molding machine and an injection compression molding method which use the compression apparatus for molding.
2. Discussion of the Background
In injection compression molding, molten resin is charged into the interior of a closed die, which is then subjected to die clamping in order to apply compression force onto the molten resin, to thereby complete molding.
In such injection compression molding, since low pressure is employed for injection of resin, no warpage or distortion is imparted to a molded article. Therefore, a molded article having excellent shape is advantageously manufactured even if the molded article has a small wall thickness.
Generally, a molding machine for injection compression molding includes a die composed of a movable mold and a stationary mold, a mold clamping apparatus, and a compression apparatus. The movable mold is movably provided in the molding machine. The stationary mold is fixed to the molding machine. The mold clamping apparatus advances the movable mold toward the stationary mold. The compression apparatus is adapted to compress molten resin which has been charged into the die.
Japanese Patent Application Laid-Open (kokai) Nos. 57-95429 and 60-122128 discloses conventional compression apparatuses. In these apparatuses, a movable portion for adjusting the volume of a die is provided in the interior of the die; and the movable portion is advanced via a pin which abuts the movable portion in order to reduce the volume of the die, to thereby compress molten resin charged into the die.
Such apparatuses disadvantageously have limited utility, since they do not enable injection compression molding by use of an ordinary die containing no movable portion.
To solve the above-mentioned problem, the present inventor has proposed a compression apparatus (Japanese Patent Application Laid-Open (kokai) No. 7-164500). As shown in FIG. 16, the proposed compression apparatus 95 is a unit comprising a mechanism for pushing a movable mold 91 toward a stationary mold 92, and is removably disposed between a die 93, composed of the movable mold 91 and the stationary mold 92, and a mold clamping apparatus 94. A clearance a shown in FIG. 16 has the same purpose as that of a clearance a shown in FIG. 1 as described below.
As shown in FIG. 17, the compression apparatus 95 has slant members 97 and 98 arranged along the compression direction. Each of the slant members 97 and 98 has a slant surface 96 slanted with respect to the compression direction. Of these slant members, the slant members 98 located at the side of the mold clamping apparatus 94 are moved perpendicular to the compression direction, to thereby generate compression force.
A plurality of pairs each comprising one slant member 97 and one slant member 98 are provided. As shown in FIG. 18, the slant members 98 which are made movable are arranged so as to form a square. A rack 99 for synchronization is provided on a side face of each of the slant members 98. A gear 100 for engaging the racks 99 is provided in the space surrounded by the slant members 98. The racks 99 and the gear 100 constitute a synchronization mechanism 101.
In the above-described compression apparatus 95, there is employed a mechanism which generates compression force by pushing the entirety of the movable mold 91. Therefore, the compression apparatus enables injection compression molding by use of an ordinary die containing no movable portion, so that utility is enhanced.
Also, since the motions of the slant members 98 are synchronized by means of the synchronization mechanism 101, no bias is produced in pushing force generated by the slant members 98, so that uniform compression force can be applied to the molten resin. As a result, a molded article having excellent dimensional precision and appearance is reliably molded.
However, the above-described compression apparatus 95 has an intricate structure in which the slant members 98 are arranged around the gear 100 of the synchronization mechanism 101, and each of the slant members 98 is engaged with the gear 100. Further, since a large drive force is applied to the slant members 98, a large torque is applied to the gear 100 of the synchronization mechanism 101. Therefore, the gear 100 must have a relatively large diameter, resulting in difficulty in reducing the size and weight of the compression apparatus.
Especially, in the case of molding of a large article, the compression apparatus may become considerably large and heavy, depending on the shape of the molded article. In this case, the compression apparatus cannot be attached to a molding machine.